Multiple-carrier system or carrier aggregation system indicates the system that uses at least one aggregated carrier having a bandwidth smaller than a target bandwidth in configuring a broadband to support. When the at least one carrier having the bandwidth smaller than the target bandwidth is aggregated, a band of the aggregated at least one carrier may be limited to a bandwidth used by a previous system for the backward compatibility with the previous system. For instance, the legacy 3GPP LTE system supports bandwidths of 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. And, LTE-A (LTE-advanced) system is set to support a bandwidth greater than 20 MHz using the bandwidths supported by the LTE. Alternatively, it may be able to support carrier aggregation by defining a new bandwidth irrespective of a bandwidth used by a previous or legacy system.
Multi-carrier is the name that may be interchangeably used together with carrier aggregation or bandwidth aggregation. And, the carrier aggregation may inclusively indicate contiguous carrier aggregation and non-contiguous carrier aggregation (spectrum aggregation).
In order to use multi-carrier efficiently, a technique for one higher layer (e.g., a series of layers including MAC layer, RRC layer and PDCP layer) to manage PHY layers for controlling several carriers respectively is explained as follows.
FIG. 1 is a diagram for one example of a concept for a base station to manage downlink component carriers and FIG. 2 is a diagram for one example of a concept for a user equipment to manage uplink component carriers. For clarity and convenience of the following description, a higher layer in FIG. 1 or FIG. 2 is schematized as a MAC.
FIG. 3 is a diagram for describing a concept for one MAC to manage multiple carriers in viewpoint of a transmission by a base station. And, FIG. 4 is a diagram for describing a concept for one MAC to manage multiple carriers in viewpoint of a reception by a user equipment. In the drawings, in order to effectively transmit and receive multiple carriers, both a transmitter and a receiver should be capable of transmitting and receiving the multiple carriers.
In brief, one MAC manages and operates at least one frequency carrier to transmit and receive. Since frequency carriers managed by one MAC need not to be contiguous with each other, resource management can advantageously become more flexible. One PHY in FIG. 3 or FIG. 4 is set to mean one component carrier for clarity and convenience of the following description. In this case, it may be not mandatory for one PHY to mean an independent RF (radio frequency) device. Generally, one independent RF device means one PHY, by which the one independent RF device is non-limited. Alternatively, one RF device may include several PHYs.
FIG. 5 is a diagram for describing a concept for at least one MAC to manage multiple carriers in viewpoint of a transmission by a base station. And, FIG. 6 is a diagram for describing a concept for at least one MAC to manage multiple carriers in viewpoint of a reception by a user equipment. FIG. 7 is a diagram for describing a concept for at least one MAC to manage multiple carriers in viewpoint of a transmission by a base station. And, FIG. 8 is a diagram for describing a concept for at least one MAC to manage multiple carriers in viewpoint of a reception by a user equipment.
In addition to the structures shown in FIG. 3 and FIG. 4, multiple carriers can be controlled not by one MAC but by at least one or more MACs, as shown in FIGS. 5 to 8.
Referring to FIG. 5 and FIG. 6, each carrier can be 1-to-1 controlled by each MAC. Referring o FIG. 7 and FIG. 8, each carrier can be 1-to-1 controlled by each MAC for some carriers and the rest of at least one or more carriers can be managed by one MAC.
The above-described system is the system that includes at least one or more carriers of which number ranges 1 to N. And, each of the carriers may be usable contiguously or non-contiguously. This is applicable irrespective of uplink or downlink. In case of TDD system, N multiple-carriers are configured to operate in a manner that UL (uplink) and DL (downlink) transmissions are included in each carrier. In case of FDD system, multiple carriers are configured to be usable in each of UL (uplink) and DL (downlink).
Although a UL and a DL are set to differ from each other in bandwidth in a legacy system, transmission and reception in a single carrier are basically supported. Yet, the system of the present invention may be able to operate multiple carriers through the carrier aggregation mentioned in the foregoing description. Besides, FDD system may be able to support asymmetric carrier aggregation in which UL and DL differ from each other in the number of aggregated carriers and/or a carrier bandwidth.
Carrier aggregation, in which at least two component carriers are aggregated, may be taken into consideration to support a wider transmission band (e.g., 100 MHz) and spectrum aggregation.
In accordance with performance, a user equipment may be able to simultaneously receive or transmit one component or a plurality of component carriers.
A user equipment having the reception and/or transmission capability for carrier aggregation is able to simultaneously perform reception and/or transmission via multiple component carriers. And, a legacy user equipment is able to perform reception or transmission via a single component carrier.
When the number of aggregated component carriers of UL is equal to that of aggregated component carriers of DL, it may be possible to configure all component carriers of a legacy system. Yet, a component carrier, which does not take compatibility into consideration, is not excluded by the present invention.
It may be possible for a user equipment to be configured to aggregate component carriers of which number and band in UL are different from those in DL, respectively. In typical TDD, the number and band of component carriers in UL may be equal to those of component carriers in DL.
Regarding MAC-PHY (media access control-physical) interface, in viewpoint of a user equipment, assuming that there is no space multiplexing, one HARQ (hybrid automatic repeat request) entity may exist in each scheduled component carrier. Each transport block is mapped to a single component carrier. And, a user equipment may be simultaneously scheduled for a plurality of component carriers.
In symmetric carrier aggregation (i.e., a case that the number of aggregated UL component carriers is equal to that o DL component carriers), assuming that in a process for attaching an index to a PUCCH resource, all component carriers maintain compatibility with a legacy system, such principle of a legacy system (e.g., LTE Rel-8) as ACK/NACK bundling, channel selection scheme, ACK/NACK multiplexing via multi-sequence modulation is extended to be simplified. In this case, the ACK/NACK bundling is the scheme used to efficiently transmit to feed back a plurality of ACK/NACK informations and means to process and transmit a plurality of the ACK/NACK informations by using a logical AND operation or a logical OR operation. For instance, the bundling by using the logical AND operation is performed in a following manner. First of all, if at least one NACK exists in a plurality of ACK/NACK's, a NACK signal is transmitted. Secondly, only if a response of every signal is ACK as a result of decoding, ACK is transmitted. For another instance, the bundling by using the logical OR operation is performed in a following manner. First of all, if at least one ACK exists in a plurality of ACK/NACK's, an ACK signal is transmitted. Secondly, only if a response of every signal is NACK as a result of decoding, NACK is transmitted.
For clarity and convenience of the following description, when a PDCCH is transmitted on DL component carrier #0, it is assumed that a corresponding PDSCH is transmitted on DL component carrier #0. Yet, it is apparent that the corresponding PDSCH can be transmitted on another DL component carrier by applying cross-carrier scheduling.
For clarity and convenience of the following description, when a PDCCH is transmitted on DL component carrier #0, it is assumed that a corresponding PDSCH is transmitted on DL component carrier #0. Yet, it is apparent that the corresponding PDSCH can be transmitted on another DL component carrier by applying cross-carrier scheduling.
A control region is constructed with a logical CCE sequence including a plurality of control channel elements (CCEs). In the following description, the CCE sequence is a set of all CCEs configuring a control region in a single subframe. The CCE corresponds to a plurality of resource element groups. For instance, a CCE may correspond to 9 resource element groups. The resource element group is used in defining to map a control channel by a resource element. For instance, one resource element group may be configured with 4 resource elements.
A plurality of PDCCHs may be transmitted within a control region. The PDCCH carries such control information as scheduling allocation and the like. The PDCCH is carried on an aggregation of one or several contiguous CCEs (control channel elements). A format of PDCCH and the number of bits of available PDCCH are determined in accordance with the number of CCEs configuring the CCE aggregation.
In the following description, the number of CCEs used for PDCCH transmission is called a CCE aggregation level. And, the CCE aggregation level is a CCE unit to search for PDCCH. Moreover, a size of the CCE aggregation level is defined as the number of contiguous CCEs. For instance, the CCE aggregation level may include the element of {1, 2, 4, 8}.
Table 1 shows examples of a PDCCH format and the number of bits of available PDCCH in accordance with a CCE aggregation level.
TABLE 1PDCCHCCE aggregationNumber of resourceNumber offormatlevelelement groupsPDCCH bits01 9 72121814424362883872576
Control information carried on PDCCH is called downlink control information (hereinafter abbreviated DCI). The DCI carries UL schedule information, DL scheduling information, system information, UL power control command, control information for paging, control information for indicating a random access resource (random access channel: RACH) and the like. And, the DCI may be able to carry control information for indicating SPS (semi-persistent scheduling) activation. Moreover, the DCI may be able to carry control information for indicating SPS (semi-persistent scheduling) deactivation. In this case, the semi-persistent scheduling may be used for UP or DL VoIP (voice over internet protocol) transmission.
DCI formats may include Format 0 for PUSCH (physical uplink shared channel) scheduling, Format 1 for scheduling of one PDSCH (physical downlink shared channel) codeword, Format 1A for compact scheduling of one PDSCH codeword, Format 1B for scheduling of rank-1 of a single codeword in space multiplexing mode, Format 1C for very compact scheduling of DL-SCH (downlink shared channel), Format 1D for PDSCH scheduling in multi-user space multiplexing mode, Format 2 for PDSCH scheduling in closed-loop space multiplexing mode, Format 2A for PDSCH scheduling in open-loop space multiplexing mode, Format 3 for transmission of TPC (transmission power control) command for UL channel, and Format 3A for transmission of TPC (transmission power control) command for UL channel.
FIG. 9 is a flowchart for a configuration of PDCCH.
Referring to FIG. 9, a base station (BS) generates control information in accordance with a DCI format. The base station is able to select one DCI format from a plurality of DCI formats (DCI format 1, DCI format 2 . . . DCI format N) in accordance with a control information scheduled to be sent to a user equipment (UE). In a step S710, a cyclic redundancy check (hereinafter abbreviated CRC) for error detection is attached to the control information generated in accordance with each of the corresponding DCI formats. In this case, the CRC is masked with an identifier (e.g., this is called a radio network temporary identifier (RNTI)) in accordance with an owner or usage.
In case of PDCCH for a specific user equipment, the CRC can be masked with a unique identifier of the user equipment, e.g., C-RNTI (Cell-RNTI). In particular, the CRC may be scrambled together with the unique identifier of the user equipment. The RNTI for the specific user equipment may include one of a temporary C-RNTI, a semi-persistent C-RNTI and the like. The temporary C-RNTI is a temporary identifier of a user equipment and may be usable for the duration of a random access procedure. And, the semi-persistent C-RNTI may be useable to indicate semi-persistent scheduling activation.
In case of PDCCH for a paging message transmitted on PCH, the CRC may be masked with a paging identifier, e.g., a P-RNTI (Paging-RNTI).
In case of PDCCH for system information transmitted on DL-SCH, the CRC can be masked with a system information identifier, e.g., SI_RNTI (System Information-RNTI). In case of PDCCH for indicating a random access response in response to a transmission of a random access preamble of a user equipment, the CRC can be masked with RZ-RNTI (Random Access-RNTI). Table 2 shown in the following shows examples of an identifier that masks PDCCH.
TABLE 2TypeIdentifierDescriptionUE-specificC-RNTI, temporaryused for a unique UE identificationC-RNTI,semi-persistentC-RNTICommonP-RNTIused for paging messageSI-RNTIused for system informationRA-RNTIused for random access response
If one of the C-RNTI, the temporary C-RNTI and the semi-persistent C-RNTI is used, the PDCCH carries control information for a corresponding specific user equipment. If another RNTI except the C-RNTI, the temporary C-RNTI and the semi-persistent C-RNTI is used, the PDCCH carries common control information received by every user equipment within a cell.
In a step S720, coded data is generated in a manner of performing channel coding on the CRC attached control information. In a step S730, a rate matching in accordance with a CCE aggregation level assigned to the PDCCH format is performed.
In a step S740, modulated symbols are generated in a manner of modulating the coded data. In particular, the modulated symbols configuring one PDCCH may have the CCE aggregation level set to one of 1, 2, 4 and 8. In a step S750, the modulated symbols are mapped to physical resource element (RE) [CCE to RE mapping].
FIG. 10 is a flowchart of PDCCH processing.
Referring to FIG. 10, in a step S810, a user equipment maps physical element to CCE [CCE to RE demapping]. In a step S820, since the user equipment is not aware of a specific CCE aggregation level to receive PDCCH, the user equipment performs demodulation on each CCE aggregation level. In a step S830, the user equipment performs a transmission rate dematching on a demodulated data. Since the user equipment is not aware what kind of control information having a specific DCI format it should receive, the user equipment performs the transmission rate dematching on each of the DCI formats. In a step S840, channel decoding is performed on the rate-dematched data in accordance with a code rate and CRC is then checked to detect whether error is generated. If the error is not generated, it means that the user equipment has detected its PDCCH. If the error is generated, the user equipment keeps performing blind decoding on another DCI format. In a step S850, after the user equipment has detected the PDCCH of its own, the user equipment removes CRC from the decoded data and then acquires control information necessary for itself.
A plurality of PDCCHs multiplexed for a plurality of user equipments can be transmitted in a control region of one subframe. A user equipment monitors the PDCCHs. In this case, the ‘monitoring’ means that the user equipment attempts to decode each of the PDCCHs in accordance with a monitored DCI format. In the control region allocated within the subframe, a base station does not provide the user equipment with information indicating where the corresponding PDCCH is located. The user equipment finds the PDCCH of its own by monitoring a set of PDCCH candidates in the subframe. This is called blind decoding. Trough the blind decoding, the user equipment performs both identification of the PDCCH transmitted to itself and decoding of the control information carried on the corresponding PDCCH. For instance, if CRC error is not detected from de-masking the corresponding PDCCH from its C-RNTI, the user equipment may detect its PDCCH.
In order to effectively reduce overhead of the blind decoding, the number of DCI formats carried on PDCCH is limitedly defined. The number of the DCI formats becomes smaller than types of heterogeneous control informations transmitted on PDCCH. The DCI format may include a plurality of different information fields. In accordance with the DCI format, a type of an information field configuring the DCI format, the number of information fields, the number of bits of each information field and the like vary. And, a size of control information matched with the DCI format varies in accordance with the DCI format. PDCCH transmission of each of the various control informations is performed using one of the limited number of the DCI formats. In particular, a random DCI format may be usable for the transmission of at least two control informations of different types. Hence, if a value of an information field of a DCI format is embodied into a specific value, partial information fields among a plurality of information fields may not be necessary for a control information. In particular, detailed values may not be defined in partial fields among a plurality of the information fields that configures the DCI format. Each of the partial information fields configuring the DCI format becomes a reserved field and may be then reserved in a state having an arbitrary value. This is to enable heterogeneous control informations of a plurality of types to be size-adapted into one DCI format [size adaptation]. Thus, if a reserved field exists in control information transmission, a base station inefficiently wastes transmission energy and transmission power for a corresponding reserved field transmission that is not used for any function. Therefore, when a control information is generated by being matched with a DCI format, the demand for a method of utilizing an unused information field among a plurality of information fields configuring the DCI format is rising.
FIG. 11 shows one example of a method of utilizing an unused information field among a plurality of information fields configuring a DCI format.
Referring to FIG. 11, control informations A, B and C, which differ from each other in type, are grouped together to use one DCI format. The control informations A, B and C are matched with one DCI format. In this case, the DCI format consists of a plurality of different information fields. The control information A is embodied in a manner that a specific value is given to all information fields. Each of the control informations B and C is embodied in a manner that a specific value is given to partial information fields of the corresponding DCI format. An information bit size of the control information A is the biggest within the group. This is because the control information A corresponds to a case that all information fields of the corresponding DCI format are meaningfully configured. The information bit size of the control information A becomes a reference information bit size. In order to have the size equal to the reference information bit size, the control information B or C has null information added thereto. Through this, each of the control informations in the group is fixed to the same information bit size.
Thus, heterogeneous control informations of a plurality of types are grouped to be matched with a randomly designated DCI format. Each individual control information is embodied by mapping a specific value to an information field configuring a corresponding DCI format. Random control informations in a group can be embodied by giving a specific value to all information fields of the corresponding DCI format. On the contrary, other control information in the group can be embodied by giving a specific value to partial information fields of the corresponding DCI format. In particular, other information fields of the corresponding DCI format do not need to be used to embody control information. In this case, a total size of the information fields used to embody the control information may be defined as an information bit size. The information bit size of the former control information is the biggest, whereas the information bit size of the latter control information is relatively small.
An information bit size in case of embodying a control information by giving a specific value to all information fields of a DCI format is set as a reference information bit size. The reference information bit size means a total size of the information fields configuring the DCI format or a size of the DCI format itself. If other control information in the group has an information bit size smaller than the reference information bit size, null information is added to have the information bit size equal to the reference information bit size. In particular, when a specific control information is embodied by designating a value to partial information fields among all information fields designated in the DCI format, the rest of the information fields failing to have a value designated thereto are used as the null information. In this case, the information field used as the null information may be called an error check field.
Null information is the information that is added to enable a control information to have a size equal to a reference information bit size of a matched DCI format. When a control information is generated in accordance with a DCI format, an unused partial information field may be used as null information. The null information has a specific value. For instance, an information field used as the null information may be set to a value of all ‘o’ bits or all ‘1’ bits. Alternatively, a field used as the null information may be designated to a value of a binary code sequence already known to both a base station and a user equipment. This binary code sequence may be named a binary scramble code sequence. For example, this code sequence can be generated on the basis of a method of generating a binary bit sequence already known to both a base station and a user equipment, an m-sequence or a gold sequence generated by a base station and a user equipment using the same input parameter.
An information field used as a null information may be set in advance between a base station and a user equipment. Alternatively, a base station may be able to inform a user equipment of an information on an information field used as a null information through RRC signaling or system information.
When a user equipment monitors PDCCH through CRC error detection, the following errors may occur. First of all, the user equipment may recognize PDCCH belonging to another user equipment as its PDCCH. Secondly, if demaksing is performed using an RNTI different from an actual RNTU, the user equipment may not detect an CRC error but may recognize that decoding is correctly performed. Such an error is called a false positive error. In order to lower the occurrence possibility of the false positive error, null information may be utilized as a probe for a virtual CRC check or an additional error check.
As a radio resource scheduling scheme, there is a dynamic scheduling scheme, a persistent scheduling scheme, a semi-persistent scheduling (SPS) scheme. The dynamic scheduling scheme is the scheme of requesting scheduling information each time data is transmitted or received. On the other hand, the persistent scheduling scheme is the scheme of not requesting scheduling information via a control signal each time data is transmitted or received, using preset information. The semi-persistent scheduling scheme is the scheme of not requesting scheduling information via a control signal each time data is transmitted or received for a semi-persistent scheduling interval. The semi-persistent scheduling interval is initiated by a reception of control information indicating a semi-persistent scheduling activation and may expire by a reception of control information indicating a semi-persistent scheduling deactivation. Alternatively, the semi-persistent scheduling interval may be set through an RRC signaling.
FIG. 12 is a flowchart for a DL data transmission using a dynamic scheduling scheme. A base station transmits DL grant on PDCCH to a user equipment each time transmitting DL data on PDSCH. Using the DL grant received on the PDCCH, the user equipment receives the DL data transmitted on the PDSCH. Therefore, it is advantageous in that the base station is able to schedule a radio resource appropriately in accordance with a DL channel condition.
FIG. 13 is a flowchart for a UL data transmission using a dynamic scheduling scheme. Before a user equipment transmits UL data on PUSCH, the user equipment receives allocation of a radio resource via a UL grant from a base station. In doing so, the UL grant is transmitted on PDCCH.
VoIP (Voice over IP) is the service of transmitting voice data via IP (internet protocol) and is a method of providing voice data, which was provided in a CS (circuit switched) domain, in a PS (packet switched) domain. The VoIP transmits voice data by connection-less, whereas the CS based voice service transmits voice data by maintaining an end-to-end connection. Hence, the VoIP is advantageous in using a network resource very efficiently.
Owing to the ongoing development of wireless communication technology, user data increases very fast and the conventional CS based services tend to be replaced by the PS based service considerably in order to user the limited network resources efficiently. In this context, the VoIP is being developed. And, it is expected that all voice services will be provided in the future via VoIP in most of wireless communication systems.
In order to effectively provide the PS based voice service, RTP (real-time transport protocol) has been developed and RTCP (RTP control protocol) for controlling the RTP has been developed as well. As the RTP carries time stamp information on each packet, it may be able to solve the Jitter problem. As a loss of RTP packet is reported via the RTCP, it may be able to lower FER (frame error rate) through a rate control. SIP (session initiation protocol), SDP (session description protocol) and the like have been developed as well as RTP/RTCP, it may be able to considerably solve a delay problem in a manner of maintaining an end-to-end virtual connection.
FIG. 14 is a diagram for one example of a traffic model in VoIP.
Referring to FIG. 14, types of voice packets generated in VoIP can be classified into a packet generated from a talk spurt and a packet generated from a silence period. For instance, assuming 12.2 kbps AMR (adaptive multi-rate), RTP packet is generated in the talk spurt by period of 20 ms and has a size of 35˜49 bytes. In the silence period, RTP packet is generated by period of 160 ms and has a size of 10˜24 bytes.
In such a voice service as VoIP, if a packet is generated by predetermined periods, the generated packet has a relatively small and uniform size. Hence, the VoIP generally uses a persistent scheduling scheme or a semi-persistent scheduling scheme. In case of the persistent scheduling scheme, a radio resource is persistently allocated by predicting it in a radio bearer setting process and a packet is correspondingly transmitted or received without a control signal containing scheduling information. When data is transmitted or received by the persistent scheduling scheme, since a preset radio resource is used instead of providing scheduling information, a channel condition is not taken into consideration at a timing point of transmitting or receiving data. Hence, if the channel condition is changed, a transmission error rate may be increased. The VoIP sets a talk spurt to a semi-persistent scheduling interval and is suitable for using the semi-persistent scheduling scheme.
FIG. 15 is a flowchart for a DL data transmission using semi-persistent scheduling. A base station transmits control information indicating a semi-persistent scheduling activation of resource allocation information to a user equipment on PDCCH. In the semi-persistent scheduling interval, the user equipment may be able to receive VoIP data from the base station via PDSCH using the resource allocation information.
FIG. 16 is a flowchart for a UL data transmission using semi-persistent scheduling. A base station transmits control information indicating a semi-persistent scheduling activation of resource allocation information to a user equipment on PDCCH. In the semi-persistent scheduling interval, the user equipment may be able to transmit VoIP data to the base station via PUSCH using the resource allocation information.
First of all, a method of transmitting control information indicating a semi-persistent activation via DCI format 0 is explained. Via the DCI format 0, control information for scheduling of PUSCH and control information indicating a semi-persistent scheduling activation can be transmitted. In this case, the semi-persistent activation may be usable for UL VoIP transmission.
Table 3 shows examples of control information carried on DCI format 0.
TABLE 3Information Fieldbit(s)(1)Flag for format0/format1A differentiation1(2)Hopping flag1(3)Resource block assignment and hopping |log2(NRBUL(NRBUL + 1)/2|resource Allocation(4)Modulation and coding scheme and 5redundancy Version(5)New data indicator1(6)TPC command for scheduled PUSCH2(7)Cyclic shift for DM RS3(8)UL index (TDD)2(9)CQI request1
DCI format 0 includes a plurality of information fields. The information fields include (1) flag field, (2) hopping flag field, (3) resource block assignment and hopping resource allocation field, (4) MCS (Modulation and Coding Scheme) and redundancy version field, (5) new data indicator field, (6) TPC command field, (7) cyclic shift field, (8) UL index field, and (9) CQI request field. A bit size of each of the information fields is just exemplary, by which a bit size of a field is non-limited.
The flag field is the field for differentiation between format 0 and format 1A. The resource block assignment and hopping resource allocation field may have a bit size of field vary in accordance with hopping PUSCH or non-hopping PUSCH. The resource block assignment and hopping resource allocation field for the non-hopping PUSCH provides |log2(NRBUL(NRBUL+1))/2| bits to a resource allocation of a 1st slot in a UL subframe. In this case, NULRB indicates the number of resource blocks included in a UL slot and is dependent on a UL transmission bandwidth set by a cell. The resource block assignment and hopping resource allocation field for the hopping PUSCH provides |log2(NRBUL(NRBUL+1))2|−NUL—hop bits to a resource allocation of a 1st slot in a UL subframe.
Control information of channel assignment for PDSCH is represented using all the fields mentioned in the above description. Hence, DCI format 1A for the channel assignment for PDSCH becomes a control information having an information size that becomes a reference.
If the number of information bits of the format 0 is smaller than that of information bits of the format 1A, ‘0’ is appended to the format 0 until a payload size of the format 0 becomes equal to that of the format 1A.
Control information for scheduling of PUSCH is represented using all the fields mentioned in the above description. Hence, DCI format 0 for the scheduling of PUSCH becomes the control information having a reference information bit size.
Since the current LTE system supports 4×4 MIMO transmission in DL but does not support MIMO transmission in UL, a DCI format for the UL MIMO transmission does not exist. So to speak, a DL grant for DL MIMO exists and a UL grant (DCI format 0) for UL transmission of a single antenna exists only.
Therefore, in order to support 8×8 MIMO transmission in DL and 4×4 MIMO transmission in UL, a definition of a new DCI format for UL MIMO is requested.
Generally, since the increase of DCI formats raises a count of blind decodings that should be performed by a user equipment, complexity of the user equipment is increased correspondingly.
Therefore, a method of differentiating a DL grant and a UL grant from each other without increasing complexity of a user equipment in a manner of sharing formats of the DL grant and the UL grant not to raise a count of blind decodings is requested.